Speedo gear options

[Nustad 510]

Hi all,

I have a dogleg five speed gearbox in my 510 with an R180 diff and 4.11 gears. What speedo drive are you people running to keep the speedo reading correctly? I have a red 20 tooth gear from a Zed car, however, the alloy speedo drive housings are different between the long and short tail gearboxes. The early speedo gears are easily drifted off the shaft but later ones do not seem to come off. Any help on how you overcome this would be great. Thanks, Shaun.

[datzenmike]

The speedometer cable is made to spin faster or slower by varying the plastic gears on the pinion sleeve. A Z car 71B pinion will not fit or work on a 63A dogleg. 

 

 

What color or number of teeth pinion gear is in the dogleg right now and how far off is the speedometer at 100K??? Knowing this will tell us which direction to go and how much.

 

Example

If you have a Red 20 tooth in now and are reading 105 KPH at an actual 100KPH you'r 5% fast. The speedometer cable is spinning 5% too fast and needs to be slowed down. By running a pinion with more teeth it will take more transmission turns to turn it. The difference between a 20 and a 21 tooth gear is 5% and what do you know? this provides the perfect correction factor. Now I don't know what's in your dogleg, I would guess around 17 tooth. Below is the correction in % between the tooth counts. 

16-17.... 6.25%

17-18.... 5.9%

18-19.... 5.5%

19-20.... 5.26%

20-21.... 5%

 

Each tooth change increases or reduces 'about' 5.5%. Obviously if you should be out 10% then a 2 tooth change is needed. Like a 17 to a 19 would be 11.7% (you'll never get it exact, but 1.7% out at 100K isn't that much.

 

Where will you find different 'gears'? Well the F4W63 4 speeds with the removable bottom pan on it, used in most 610, 710, 510, A10s should fit, and the dogleg was an option in the A10 and the B-210.

[AtomChurch]

14 hours ago, datzenmike said:

The speedometer cable is made to spin faster or slower by varying the plastic gears on the pinion sleeve. A Z car 71B pinion will not fit or work on a 63A dogleg. 

 

 

What color or number of teeth pinion gear is in the dogleg right now and how far off is the speedometer at 100K??? Knowing this will tell us which direction to go and how much.

 

Example

If you have a Red 20 tooth in now and are reading 105 KPH at an actual 100KPH you'r 5% fast. The speedometer cable is spinning 5% too fast and needs to be slowed down. By running a pinion with more teeth it will take more transmission turns to turn it. The difference between a 20 and a 21 tooth gear is 5% and what do you know? this provides the perfect correction factor. Now I don't know what's in your dogleg, I would guess around 17 tooth. Below is the correction in % between the tooth counts. 

16-17.... 6.25%

17-18.... 5.9%

18-19.... 5.5%

19-20.... 5.26%

20-21.... 5%

 

Each tooth change increases or reduces 'about' 5.5%. Obviously if you should be out 10% then a 2 tooth change is needed. Like a 17 to a 19 would be 11.7% (you'll never get it exact, but 1.7% out at 100K isn't that much.

 

Where will you find different 'gears'? Well the F4W63 4 speeds with the removable bottom pan on it, used in most 610, 710, 510, A10s should fit, and the dogleg was an option in the A10 and the B-210.

 

 

A stock 1970 510 speedo cog pinion does fit on a 90s era KA trans.. What they did was keep the same design for the digital sending unit and rotate the offset just about 180 degrees. I have gotten the stock speedo to work mechanically by simply rotating the speed sending unit until it fits in and then cutting a new retaining slot where one needs to be to correspond to the stock bolt hole in the transmission. In the five ten you need a longer speedo cable because of the longer ka trans.

 

if you dont care about stock speedos maybe you could just do that in reverse? Take the later model digital speed sending unit and adapt it to a speedo that is adjustable? I don't know for sure, just an idea I have had floating around.

Its not too hard to pop the needle off and mount a stock faceplate to newer speedo internals.

 

For myself, since I have never gotten different gears to be accurate throughout the range of my engine,trans,diff...( I have a dogleg in my 521.)

I shoot for my speedo to be accurate at around 60, rather the freeway speed near me. Simple so I know when I am speeding for sure, when I pass that cop pointing his gun shaped speed sensing device at me.. Otherwise I just drive like I normally drive and ignore the speedo. I care more about the tach personally. In America we have digital speed signs; In the past I find one close to my house, and test out the speedometer by driving past it at certain speeds. It is also still legal (as for helping a driver) for someone in America to ask a nice policeman to drive the speed limit and have you follow them so you can check your speedometers accuracy.. might be able to get out of a ticket by politely asking for that as well.
I mean you just swapped transmissions and put bigger tires on, even though it felt shaky at the "highway" speeds, you were just trying to get home so you could adjust things. All you "have" is your guages and they may have been affected by the mods..
 

[datzenmike]

 

Don that with 71B transmissions. I have a '79 zx 5 speed but fitted with a 22 tooth 720 pinion. Had to nick it to make it work.

 

Earlier 4 speed on left. 71B on right

[Nustad 510]

Thanks people,

 

Counted some teeth.  My short tail 63a dogleg box has a 16 tooth speedo gear, as does my original 510 4 speed box.  At this point I will wait for my new 14 inch rims and tyres and check with GPS, then see where things are at.  Mike, I took exactly the same picture when explaining this issue to a friend. 71B speedo drive assemblies are shorter.

 

Cheers, Shaun